One Man's Trash

Waste materials can be a producer's treasure.

To professor Christian Meyer, chairman of Columbia University's Department of Civil Engineering and Engineering Mechanics, what's new in concrete starts with what is old.

Meyer began his career as an engineer and has served on many ACI committees. He chaired ACI Committee 555, Concrete with Recycled Materials, for six years. His research and analysis now focus on the benefits of recycled waste materials in producing concrete.

The concrete industry already uses waste materials such as slag, fly ash, silica fume, and ground granulated blast furnace slag. Others are still being researched, such as recycled carpet fibers and scrap metal. From Meyer's point of view, new sources for recycled material can be found anywhere there are “mountains of stuff nobody wants.”

Meyer spoke about “Concrete and Sustainable Development” during Solid States: Changing Time for Concrete. Columbia University in New York City hosted the three-day meeting of the concrete industry's most innovative minds in October. The Graduate School of Architecture, Planning and Preservation and the Department of Civil Engineering and Engineering Mechanics convened the meeting at which architects, engineers, and professors gathered to discuss “new understandings” of concrete.

Meyer sees potential concrete ingredients in post-consumer waste (glass, tires, plastic, and even garbage), industrial byproducts (wood, rice husks), and construction waste (recycled concrete, excavated rock). Each has benefits and challenges that must be explored before being used in concrete. (See table.)

Developing more sustainable concrete could make a big impact. With more than 10 billion tons produced each year worldwide, the only other commodity of which we use more is water. “The concrete industry has become a victim of its own success,” Meyer explains. “To produce 10 billion tons of concrete, you need 10 billion tons of materials...[therefore] the industry leaves a large environmental footprint, which is a tough challenge to overcome.”

Meyer is doing his part through his own research and by mentoring students who are studying concrete ingredients of the future. Olarn Pornpitaksuk, from the Bronx High School of Science, is studying phosphogypsum in concrete. Phosphogypsum is a byproduct of creating phosphoric acid, used in fertilizer, that poses a storage problem in Florida. Theo Pang, a Columbia graduate student, has studied replacing a portion of sand in concrete with mushroom substrate.

Meyer acknowledges economic feasibility may be a barrier to using recycled materials, but he believes it will get easier as virgin materials become more scarce and waste disposal costs increase. “It is not a question of ‘whether,' but ‘when' using recycled materials in construction becomes routine,” he says.